Heat exchangers are extensively used in the Chemical Process Industry. The term "shell and tube" describes a large genus of heat exchangers, and the term "floating head exchanger" specifically refers to a particular species within the shell and tube genus.
Such heat exchangers are well known to those skilled in the art, and are described in such basic reference manuals as Chemical Engineer's Handbook, Perry and Green, ed, Sixth Edition, McGraw-Hill, (1984).
As the phrase shell and tube implies, a heat exchanger "tube" (or more often, a plurality of tubes--known as a "tube bundle") is contained within a shell. The tubes are normally held in place by a "tube sheet". The term "tube sheet" refers to a flat plate having a plurality of holes which correspond in size and number to the tubes. Thus, the tube sheet defines the arrangement of the tubes in the tube bundle, according to the pattern of the holes in the tube sheet.
At one end of the tube bundle, the "fixed tube sheet" is fixed in place and is in contact with the shell. At the opposite end of the tube bundle, the "floating head tube sheet" is not fixed to the shell, thus leaving an open space between the shell and the floating head tube sheet, which is referred to as the "floating head gap".
Shell and tube heat exchangers are normally used to exchange heat between two fluid streams by passing one fluid stream through the shell (hereafter the "shell side") and a second fluid stream through the tube bundle (hereafter the "tube side").
Exchangers of this type are designed to keep the shell side fluid stream separate from the tube side fluid stream. The design is defeated, however, by leaks within the exchanger--for example, a hole in even one tube will allow some mixing of the two fluid streams. Leaks in floating head exchangers are undesirable. Such leaks may also be dangerous, depending upon the characteristics of the respective fluid streams.
The repair of leaks in an exchanger requires the shutdown and partial disassembly of the exchanger, which is a time consuming and expensive process. Thus, for reasons of safety and efficiency, it is important that leaks be properly detected and identified.
The method which is conventionally employed to detect leaks in a floating head heat exchanger involves the use of a metal "test ring", in a hydrostatic test. To begin with, the shell of the exchanger is partially disassembled to expose the floating head tubesheet. A metal test ring is then attached to the shell, and to the floating head tubesheet, so as to enclose the aforesaid floating gap. In addition, packing and a packing ring are typically employed to produce the final seal. Thus, the test ring seals the floating head gap but leaves the exterior end face of the floating head tubesheet open for inspection. Accordingly, the test ring must be very carefully fabricated to provide a close fit between the shell and the floating head tubesheet.
After the test ring is installed, water is introduced into the shell of the exchanger. If a tube is leaking, water will be visibly evident at the end of that tube.
The above test procedure has many disadvantages. It will be apparent that the test ring must conform to the dimensions of both the shell and the floating head tubesheet.
Heat exchangers are not always standard sizes and therefore a user of many different floating head exchangers is often faced with the fabrication and storage of many different test rings. The test rings are normally fabricated from a ferrous alloy, and often weigh several hundred pounds. Therefore, in addition to their inherent fabrication and storage problems, the test rings are sufficiently difficult to handle that heavy equipment is required to assist with their installation.
Accordingly, it is one object of the present invention to provide an improved apparatus for use in the detection of leaks in floating head heat exchangers.
It is another object of the present invention to provide an improved process to detect leaks in a floating head exchanger.